my DDS using square wave crystal outputs badly!!

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i have looked up the datasheet, it shows me that it can be applied both of square wave crystal or sine wave crystal. but , what i and my friend got is using square wave crystal produces sinewave badly , which contains lots of harmonic. i use TDS3034 to check the output of square wave crystal, the square wave contains some ringing, i don't know whether is my oscillograph's probe affects the result(there is some capacitor in the probe, someone told me that).
what do you think?
1. can a square wave crystal without ringing produces a nice sinewave?(in fact , the square wave itself is full of harmonic)
2. is is the ringing i see is false(falsed by oscillagraph)
3. how can i reduce the ringing?

Our Martians are beginning to learn AVR

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It is not clear what you mean by "sine wave crystal" or "square wave crystal"?

What device? You say spec sheet but spec sheet for what?

Are you using a real 10X probe or is it a couple of wires. Even if it is a good probe, ringing can be caused by ground lead too long or connected the wrong way.

Did you steal the 'scope and the probe also?

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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"sine wave crystal" means crystal oscillator which outputs sine wave, it is also used in the ACR XTAL.
datasheet means DDS's datasheet, for instance, ad9835, ad9850.
the scope is my lab's instrucment. we have not enough money to buy every software we need.
i use GCC to develop AVR, though i can use IAR freely, but i did't choose that.
nearly every electronic engineer uses protel in China, if you don't use it ,you can't follow them, it forces me to do .
you have recommended a free spice software for me, but there is little datum about that ,and no friend around me to communicate about that software.

Our Martians are beginning to learn AVR

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LTSpice (from Linear Technology) is an excellent free circuit simulator.

As for the DDS clock, the data sheet is very vague. The parts list for the evaluation board does not say. Specs say nothing. The schematic for the evaluation board hints that it uses a sine source (because of the 50 ohm load). But, almost everywhere, the data sheet refers to MCLK edges. I suspect that the clock has to meet the logic level input requirements, so I would go with a square or clipped-sine source.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Which is your problem? Harmonics and noise on the DDR output, or on the reference clock?

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The clock needs to be physically close to the DDR (1cm is a good max). Very good ground is needed. The oscillator power needs to have a GOOD bypass cap. So does the DDS (probably several, look at the layout of the evaluation board).

 

Until Black Lives Matter, we do not have "All Lives Matter"!